Disk, and counting observation apparatus for counting and observing cells through optical microscope by use of the disk

A disk for storing liquid samples containing cells and for use in counting and observing the cells through an optical microscope includes an upper member formed of a transparent material and having a plurality of liquid inlets arranged radially and adapted to introduce the corresponding liquid samples therethrough, and a plurality of air vents paired with the corresponding liquid inlets; an intermediate member having a plurality of chambers arranged radially and adapted to store the corresponding liquid samples therein, each chamber corresponding to each pair of the liquid inlet and the air vent and communicating with the liquid inlet and with the air vent; and a lower member formed of a transparent material and backing the intermediate member. The optical microscope assumes the form of an incident-light microscope.